Week 12

Question 1

What is the purpose of the collections framework in Java?

Answer 1

Provides a set of interfaces and classes that allow developers to use collections of objects in an organized /efficient way

Question 2

Java collections framework: Common operations

Answer 2

Add, remove, search for elements, iterate/sort elems, and perform opeartions like union, intersection, and difference

Question 3

Benefits of the JCF

Answer 3

Productivity, readability, maintainability, fewer bugs, greater performance, generic programming

Question 4

What is the collection interface in Java?

Answer 4

The root interface of the JCF.
Defines common methods,
Represents a group of objects called “elements”
Provides methods for adding/removing/querying elements in the collection

Question 5

What are the 4 types of collections interfaces?

Answer 5

List, Set, Queue, and Map

Question 6

List, Set, Queue, and Map. What do they represent?

Answer 6

List - Ordered collection of elements
Set - Collection of unique elements
Queue - Collection of elements with a specific ordering
Map - Represents a collection of key-value pairs

Question 7

Doe the “List” interface allow duplicate elements? How about the Set interface?

Answer 7

List allows duplicate elements, Set does not

Question 8

What does peek() do?

Answer 8

Allows you to view the top element on the stack without removing it.

Question 9

What sort of data structure style does a stack in Java follow?

Answer 9

Last in first out (Elements added to the top, removed from the top)

Question 10

Queue vs Stack

Answer 10

Queue = First in first out (Elements added tot he rear end, removed from the front)

Question 11

Does a queue provide access to elements in the middle?

Answer 11

No

Question 12

What does the map interface in Java represent?

Answer 12

A collection of key-value pairs. Each key is unique and maps to a corresponding value.

Allows elements to be accessed by using their key rather than their index or value

Question 13

add(), remove(), contains(), size(), isEmpty(), iterator(), toArray()… What do these methods have in common?

Answer 13

These methods are available in the Java Collection Interface

Question 14

What is the purpose of the diamond syntax? < >

Answer 14

It specifies generic types when creating objects of generic classes. Allows the compiler to infer the type based on the context. Improves readability.

// Before Java 7
List<String> myList = new ArrayList<String>();</String></String>

// With diamond syntax in Java 7 and later
List<String> myList = new ArrayList<>();</String>

Question 15

5 characteristics of linked lists

Answer 15

1. Dynamic size (grow or shrink at any time)
2. Efficient insertion or deletion at ends of list
3. Do not require contiguous memory (unlike arrays) more efficient for memory
4. Bad: Variable access time, needs to traverse each node from the beginning until the desired node is found
5. Bad: Do not support random access to elements (unlike arrays), the items must be accessed sequentially from head or tail of list

Question 16

This collection of elements does not allow duplicates and does not maintain an order, what is it?

Answer 16

A set

Question 17

Advantages of Set vs. List

Answer 17

Optimized organization of values for efficiency
Faster insert/removal of elems
Eliminates duplicates (efficient)

Question 18

What are the implementing classes of the set interface?

Answer 18

HashSet (based on a hash table) and TreeSet (based on a binary search tree)

Question 19

What is the purpose of the hashCode() method in a hash table?

Answer 19

Used to infer the hash code of an element, which is used to group together similar elements in the hash table

Question 20

What does the equals() method do? How is it used?

Answer 20

Determines if 2 elements in a hash table are equal. It’s used to ensure there are no duplicates allowed in the set

Question 21

What classes can be used in a hash set in Java?

Answer 21

Wrapper classes - String, Integer, Double, Point, Rectangle, Color

Question 22

This interface is used to define a natural order for objects, which is used for elements in TreeSet–where elements are kept in a sorted order

Answer 22

Comparable

Question 23

When do you use a TreeSet over a HashSet?

Answer 23

Use a TreeSet when you want to visit the sets elements in a sorted order. Otherwise, HashSet is more efficient.

Question 24

How can you declare/instantiate a set in Java?

Answer 24

Use the set interface

Set<String> name = new HashSet<>();
or
Set<String> name = new TreeSet<>();</String></String>

Question 25

A duplicate element is added to a set, what happens? When you try to remove an element that is not in a set, what happens?

Answer 25

Nothing for both. they’re ignored and not added/removed.

Question 26

Iterator<String> iter = names.iterator();
while (iter.hasNext()) {
String name = iter.next();
// Do something with name
}</String>

What does the above code do?

Answer 26

Iterates over each element in the “names” set

Question 27

Can you add an element to a set at an iterator position? How about remove?

Answer 27

You cannot add any elements, but you can remove them using “remove()”

Question 28

Maps. What is their purpose?

Answer 28

Associate keys with values, you can then sue the key to lookup values

Question 29

What is the purpose of this <String, HashSet<String>> ?</String>

Answer 29

Associates a String with a set of strings, like a thesaurus that lists synonyms for a given word

Question 30

Queues follow what order:

Answer 30

FIFO

Question 31

How are queues typically applied?

Answer 31

Print queues, print jobs are added to the queue and printed in the order they are added

Question 32

How do you initialize a queue? Where does it come from?

Answer 32

Queue<String> q = new LinkedList<>();</String>

Comes from the LinkedList class

Question 33

Can you use strings as elements in a priority queue?

Answer 33

Yes, as the elements are retrieved according to their priority, which can be determined by the natural order off the strings

Question 34

What advantage is there to declaring something a queue, rather than a linked list?

Answer 34

A queue object can only have queue operations invoked on it, maintains the integrity of the queue data structure

Question 35

ArrayLists to implement queues: yes or no?

Answer 35

No. Inefficient. Adding or removing elements at the head of the queue requires moving all other elements in the list